1. Field of the Invention
Immunoassays find wide application for the determination of a variety of drugs. Critical to the immunoassay is the reproducible binding of an antibody to the drug (hapten) of interest. Because of the nature of immunoassays, there can be a wide variety of interferences or sources of error. Where the sample is a serum sample, the serum brings with it all of the endogenous proteinaceous and polysaccharidic compositions present in serum, as well as numerous other organic compounds which are in the blood stream, either naturally or due to ingestion by the patient. These various materials can become involved, so as to interfere with the reproduceability and accuracy of the immunoassay.
The materials of usual interest, and for the purposes of the present invention, digoxin and digitoxin, are normally present in serum at extremely low concentrations, generally less than about 10.sup.-8 M. Since in carrying out the immunoassay, the serum sample will be subjected to dilution, the concentration of the digoxin in the assay sample will generally be less than 10.sup.-9 M. Thus, any significant interaction between the digoxin and digitoxin and the materials present in the serum or the antibody with the materials present in the serum can lead to erroneous results.
In attempting to enhance the accuracy and reproduceability of the immunoassay, methods must be chosen which do not introduce extraneous materials which will interfere subsequently with the assay. Furthermore, any material which is introduced must not affect the cardiac glycoside, so as to modify its binding to the antibody adversely. In addition, depending upon the particular immunoassay employed and the indicator used for detection, the method must not affect the indicator or the method for measurement in an adverse manner.
2. Description of the Prior Art
In Wong, Clin. Chen. 21, 216 (1975), an alkaline solution is employed for pre-treatment of serum in a competitive protein-binding procedure for determining serum thyroxine.